a. Field of Invention
The present invention relates generally to bridges, and more particularly, to cable stayed bridges in which cable stays are anchored to the bridge deck at one side of a pylon, extend through openings in the pylon, and are further anchored to the bridge deck at an opposite side of the pylon.
b. Description of Related Art
As shown in related art FIG. 1, in the past, cable stayed bridges have been constructed for example by anchoring cable stays 11, 12 to a bridge deck 13 by anchors 14, 15, respectively. Cable stays 11, 12 are further anchored to pylon 16 by anchors 17, 18, respectively. This conventional bridge construction technique has several drawbacks. For example, pylon 16 must be large enough to permit internal access during bridge construction for stressing operations of cable stays 11, 12, and for inspection of anchors 17, 18 after installation thereof. Installation of anchors 17, 18 is also costly and time consuming since each anchor must be individually installed and inspected thereafter. Moreover, anchors 17, 18 apply a high splitting force on pylon 16, which requires post-construction tensioning of cable stays 11, 12, and also requires significant reinforcement of pylon 16 to account for such stresses.
In the art, there currently exist various other conventional cable stayed bridge designs, as disclosed for example in U.S. Pat. Nos. 5,121,518, 4,799,279 and 4,742,591.
U.S. Pat. No. 4,799,279, for example, discloses a cable stayed bridge in which cables 36a, 36b are draped over the tops of pylon saddle sections 33a, 33b respectively, and are anchored at opposite ends of the bridge deck (see FIG. 8). It is apparent that instead of being anchored to pylon 33 as illustrated in the bridge construction technique shown in related art FIG. 1 of the present invention, cable stays 36a and 36b extend through suitable openings 38 in pylon 33. This bridge construction technique also has several similar disadvantages as compared to the bridge construction technique illustrated in related art FIG. 1 of the present invention. For example, referring to U.S. Pat. No. 4,799,279, the individual strands of cable which form cable stay 36 are in direct frictional contact with each other. This frictional interaction over a period of time causes wear, and therefore deteriorates the structural integrity of the individual cable strands and hence cable stay 36. Additionally, in the region of interaction between cable stay 36 and pylon 33, the bundle of cable strands have a tendency to bunch up and flatten themselves, which results in the strands themselves contacting and transferring a vertical compressive force onto pylon 33. Due to unpredictability of the manner in which the strands may bunch up, this vertical compressive force can be unevenly distributed and therefore result in premature deterioration of pylon 33. Moreover, this vertical compressive force also results in premature deterioration of the individual strands themselves, and is of concern in addition to the deterioration resulting from frictional interaction between the individual strands, as discussed above.